Polymer-Impregnated Wood

For many years, modified woods have been prepared by impregnation with prepolymers such as phenolic resins, followed by curing under heat and pressure. By this means considerable improvement in dimensional stability and mechanical properties may be obtained (Tarkow et a/., 1970), and products of this type are often encountered in articles of commerce, such as knife handles. In general, densely crosslinked thermosetting resins have been used in these applications. The structure of wood itself is briefly considered in Section 9.9. 

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The general phenomenon of wood modification is too broad to be covered in this monograph. However, Table 9.1 (Meyer and Loos, 1969) summarizes some of the more important processes the reader is directed to the original literature for further details. Also, for polymer-impregnated wood, see Section 11.2. 

In Table 2.2, the polymer-impregnated wood has reduced porosity, and hence is more water resistant. It is also stronger. The ionomers are included in Table 2.3, because they phase-separate like the block copolymers, and represent the limiting case of polymer I/polymer II having opposite chemical properties. One may consider these products block copolymers where the block consists of a single mer. The thermoplastic elastomers utilize the... 

Basically a polymer composite contains a polymer and a nonpolymer. While polymer composites include such compositions as foams and some types of gels, this chapter will be restricted to compositions of one or more polymers and one or more nonpolymers in the bulk state. There are a few points of overlap between blends and composites polymer-impregnated wood (where wood itself is a natural polymer blend), and organic fiber (e.g., polyester) reinforced plastics constitute examples. Compositions of special interest to this chapter include glass fiber reinforced plastics, carbon black reinforced rubber, and mineral-pigmented coatings. 

Nakagami and Yokota (1983) impregnated wood with a solution containing methacrylic acid, trifluoracetic acid and sulphuric acid, to form a covalent bond with the cell wall polymers. The methacrylic-reacted wood was then impregnated with styrene, or methylmethacrylate, to form cross-links with the reacted cell wall polymers. Improved dimensional stability was obtained, although degradation of the wood was also observed. 

A solution of styrene in methanol to impregnate wood samples, followed by polymerization, was used by Furuno and Goto (1979). Penetration of the monomer into the cell wall was determined by solvent extraction of samples after polymerization. This removed lumen located polymer, whilst leaving the cell wall bound polymer in place. This showed that the concentration of cell wall bound polymer increased in proportion to the monomer content in methanol, up to a maximum of 80% of the monomer in the solvent. No cell wall penetration was observed for treatment with neat monomer. This was also found for bulking of the wood, as determined from external dimensions of the samples. Improvements in ASE were obtained as a result of the presence of cell wall bound polymer. To achieve similar ASE values with lumen located polymer required very high polymer loadings. 

Just as wood may be impregnated with additives to improve physical properties, a variety of porous polymers also benefit from polymer impregnation. As more and more specialized applications arise, it is necessary to produce polymeric materials with very specific surface and bulk properties. The correct combination of properties may not be obtainable using a single polymer or copolymer. However, polymeric materials may be impregnated with an additive in order to modify the surface energy, bondability, hydro-philicity, and other important properties. 

The impregnation of wood by polymers with TBT functional groups offers a viable route to the preparation of bioactive wood— polymer composites with a number of advantages. Polymer impregnation may be expected to improve the strength properties and dimensional stability of wood in water. The controlled release of the toxic TBT moiety, chemically linked to the polymer located within the wood, can increase the service life of wood while ensuring min-... 

Although it is possible to incorporate organotin polymers in wood by vacuum or pressure impregnation with solutions of preformed polymer, it would be preferable to utilize monomer impregnation followed by in situ polymerization because the smaller molecular size, as well as the low viscosity of monomers, is conducive to efficient penetration of wood. Therefore, vinyl monomers in which the TBT group is chemically bonded, such as TBTMA, are used for in situ polymerization in wood (2). 

Applications of supercritical fluids for coatings and impregnation of porous and fibrous substrates (e.g., polymer fibers, wood, composite materials) with various chemicals are discussed in a number of articles (50-52). Mandel and Wang (53) reported the use of a solution of polymers diluted with SCCO2 for powder-coating applications. They reported that Ferro Corporation has developed the so-called VAMP process used in the production of powder coatings, new polymers and polymer additives, and various biomaterials, with good potential for productions of pharmaceuticals. 

The history of the research and development of polymer-impregnated mortar and concrete is the shortest of the concrete-polymer composites. The process technology for the polymer-impregnated mortar and concrete was developed by applying the concept of wood-polymer composites to cement mortar and concrete in the late 1960s. Their research and development were actively conducted in the United States [12], the European countries [13-14] and Japan [15-16] from the late 1960s to the 1970s. 

The third part, Chapters 10-12, examines the properties of composites, where one component is usually nonpoly meric. Two broad classes of composites are treated polymer-impregnated materials, such as wood or concrete, and fiber- and particle-reinforced plastics and elastomers. The approach throughout draws upon basic chemistry, materials science, and engineering. The phases discussed here tend to be large and well-defined, but the interactions at the phase interfaces remain crucial in determining properties. 

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